In this theory, it developed first among young women in the San Fernando Valley. The Frank Zappa song Valley Girl, from 1982, is a musical testament to the phenomenon. Today the most notable proponents would be the likes of Paris Hilton, New York-born but a long-term resident of Los Angeles.

Uptalk had been spotted even earlier, in 1975 by linguist Robin Lakoff, who wrote that "there is a peculiar sentence pattern… which has the form of a declarative answer to a question, and is used as such, but has the rising inflection typical of a yes-no question." But the actual term "uptalk"' wasn't used until a New York Times piece in 1993.

But in the UK many people take it as a given that the speech pattern arrived from Australia, going so far as to dub it the Australian Question Intonation. Some laymen go even further and trace the shift in British speech patterns to the arrival of soap opera Neighbours on British television in 1986.

Suddenly, a whole generation of British children and young adults were simultaneously exposed to the upward inflection. So does this claim trump the California theory?

The problem is that trends in speech can be very hard to nail down. It isn't easy to even tell how the pattern developed in either the US or Australia, let alone how it was exported. Many New Zealanders would assert the pattern started there rather than in Australia, for instance.

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A New Yorker, an Australian, a man from Northern Ireland, an Argentine and a Californian each display their own brand of uptalk

"The short answer is no-one knows," says Mark Liberman, a linguistics professor at the University of Pennsylvania. Until recently, recorded language "corpora" (bodies of words) didn't exist. Linguists often have to rely on written accounts.

Liberman and other linguists hypothesise that uptalk could date as far back as the 9th Century. "It has been suggested that this distribution of rising inflection in sentences in northern England, Scotland and Northern Ireland probably had something to do with the Scandinavian influence there," he says, "but that's just a hypothesis, like everything else."

Liberman cites Henry Sweet's A Handbook of Phonetics, a language primer from the 1870s, in which the author writes that "in Scotch the rising tone is often employed monotonously, not only in questions but also in answers and statements of facts".

Then there's the Northern Irish theory, that migration into England and Scotland could have sown the roots of uptalking. Supporters of this theory point to the occasionally sing-song tone of some Northern Irish accents.

Some Americans have a similar theory - attributing the influx of Spanish speakers into California as a possible explanation.

But migration theory would also back Australia or New Zealand as the source of the UK's uptalk. Either it was British expats travelling out to Australia and New Zealand and bringing back their manner of speaking. Or just the volume of antipodean immigration to London. The process could have been well under way before the first episode of Neighbours was even aired.

The potential spread of vocal fry could be an interesting case study. The phenomenon sees the speaker use their larynx in such way that a lower creaking or rattling quality enters their voice. There has been a great deal of discussion about it in the last few years in the US, with Kim Kardashian and Lena Dunham - when acting in TV comedy Girls - cited as examples.

One of the problems about tracing the rise of any speech pattern is that the point at which people noticed it as a "thing" does not necessarily reflect the period when it started.

We don't fully recognise it, but our manner of speech is constantly changing based on how those around us speak. And as Liberman points out, uptalk is something that's always been in our manner of speech, just not necessarily as pronounced as today. "In all variations of English," he explains," there are a set of circumstances in which rising patterns are used not in polar questions - that is, yes or no questions. Uptalk has always been available, just below the surface, because there are circumstances in which speakers not thought to be uptalkers use uptalking characteristics."

Sharyn Collins, a voice coach and elocution expert, has strong opinions on uptalk. "It's perfectly fine in Australia, New Zealand and America," she intones in a cut-glass accent. "But not here [in the UK], I believe. We've adopted it in a different way."

Some people believe the phenomenon is used by uncertain speakers hoping to win their audience over. It acts as a constant check that listeners follow - phrasing every sentence, no matter how declarative, is a subconscious begging by the speaker to be reassured. It's a use Robin Lakoff first noticed 40 years ago. "The effect," she wrote, "is as though one were seeking confirmation, though at the same time the speaker may be the only one who has the requisite information."

Winning the audience over?

"If you hear it from younger women you suspect of being excessively insecure, though it's not intended as such it can be interpreted as a form of conversational weakness," says Liberman. That's something Collins agrees with.

"It's a bit meek; a bit everyman," Collins says. "To me it's not the language of business and power. But a lot of people are using it now, including men."

Liberman suggests that uptalk is a way to assert dominance. He points to a 2005 study by Winnie Cheng and Martin Warren, who highlighted that speakers in dominant positions (the chair of a meeting, or an academic supervisor) use uptalk between three and seven times as often as the people they're talking to.

One theory as to why simple declarative statements sound like questions is that in many cases, they actually are. English is a notoriously woolly language, full of ways to say one thing and mean another. The use of uptalk could be a way to subconsciously hint that a simple statement such as "I think we should choose the left hand turn?" has a hidden meaning. Implicit within the sentence is a question: "Do you also think we should choose the left hand turn?"

Uptalk has also become more popular, Collins believes, because of our dwindling attention span. A staunch traditionalist, she believes that the rising tones we so often hear in snatches of conversation are in fact people striving to divert their companion's attention away from their mobile phone. "People are checking as they speak to make sure you're paying attention," she says.

"Whenever a student comes to me for elocution I try to eliminate uptalk," she notes, "but English is evolving and this is something I may just have to accept at some point."

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